We are investigating the mechanisms by which Rous sarcoma subsumes the following major projects:1) Analyze the complexity and constitution of the viral genome. 2.) Isolate nucleotide sequences which correspond to transforming viruses of different species. 4.) Elucidate the enzymatic mechanisms by which RNA-directed DNA polymerase transcribes the viral genome into DNA ("provirus") 5.) Isolate and characterize provirus DNA from acutely infected cells. 6.) Describe the events which lead to the integration of provirus DNA and the synthesis of viral RNA in an infected cell. 7.) Delineate the viral and cellular gene functions required for viral replication and cellular transformation. 8.) Define the controls which determine the fate of a mammalian cell infectedwith RSV. Our techniques include: 1) enzymatic synthesis ana modification of nucleic acids; 2.) molecular hybridization; 3.) immunoprecipitation; 4.) eletronmicroscopy: 5.) analysis of nucleotide composition and sequence of nucleic acids; and 6.) the use of conditional mutants of RSV/